1. Field of the Invention
The present invention relates to a photopolymerizable composition and a recording material using the same, and particularly, to a photopolymerizable composition possessing excellent sensitivity, storage stability and photo-decolorizability, and a recording material using the same.
2. Description of the Related Art
Various dry-type image-recording methods that do not use liquid developers and which produce no waste have been studied. Among such methods, a method using a photocurable composition has attracted much attention.
In this method, the photocurable composition contained in a recording material is hardened by exposing the recording material to form a latent image, and components for causing a coloring or decoloring reaction contained in an unexposed portion move by heating the recording material to form a colored image. The recording material is first exposed to light through an image draft copy, and the exposed portion is cured to form a latent image. Thereafter, by heating the recording material, components in the uncured portion (unexposed portion) move and react, thereby forming a visible image.
This method enables formation of a completely dry system that produces no waste.
Although this method can be used for recording monochrome images, it is particularly useful for recording color images. Various types of recording materials can be used for the method, a specific example being a 2-component type light and heat sensitive color-developing recording material disclosed in Japanese Patent Application Laid-Open (JP-A) No. 52-89915. This recording material is a thermosensitive color-developing type recording material, in which an electron-accepting compound and an electron-donating colorless dye are used as the two components, and which contains a photocurable composition inside and/or outside of the microcapsules.
However, even if the photocurable composition contained in the microcapsules is sufficiently cured, color development in the cured portion cannot be adequately controlled and the non-image portion tends to be colored, thereby reducing the level of contrast.
An example of a recording material capable of forming an image without color development in the non-image portion is disclosed in JP-A No. 61-123838. In the recording material, a layer containing a photopolymerizable composition including a vinyl monomer with an acidic group and a photoinitiator, a separating layer, and a layer including an electron-donating colorless dye are layered.
In this recording material, the acidic group is not thermally diffusive and thus color does not develop in the non-image portion cured by the photopolymerization reaction. However, a disadvantage is that color density is somewhat low.
A recording material disclosed in JP-A No. 60-119552 forms a negative image in the same manner. In the recording material, a photopolymerizable composition, including a monomer or prepolymer, which is for bleaching a dye, and a photoinitiator, is isolated from a dye to be bleached by the monomer or prepolymer. However, this recording material has the same disadvantage of low color density as observed in the above-mentioned recording material, despite the fact that the non-image portion is left uncolored.
In view of the above disadvantages, the applicant has proposed recording materials in JP-A Nos. 3-87827 and 4-211252, which exhibit reduced color development in the non-image portion and high color density. The recording material disclosed in JP-A No. 3-87827 is a 2-component type light and heat sensitive color-developing recording material, in which one of the two components is enclosed in microcapsules, and the other is used as a curable compound of the photocurable composition or contained on the exterior of the microcapsules with the photocurable composition. The recording material disclosed in JP-A No. 4-211252 is a light and heat sensitive recording material, in which microcapsules enclosing an electron-donating colorless dye, and a photocurable composition, disposed on the exterior of the microcapsules, containing an electron-accepting compound, a polymerizable vinyl monomer and a photoinitiator are applied to form a layer.
To record a color image on such light and heat sensitive recording materials, a plurality of recording layers which have different photosensitive wavelengths and produce different colors are layered on a support.
The above-mentioned recording materials proposed by the applicant are examples of multicolor, light and heat sensitive recording materials. Specifically, in the multicolor material, a 1st recording layer that is sensitive to light with a center wavelength λ1 to produce a 1st color; an intermediate layer absorbing the light with the center wavelength λ1; a 2nd recording layer that is sensitive to light with a center wavelength λ2 to produce a 2nd color different from the 1st color; . . . ; an intermediate layer absorbing light with a center wavelength λi−1; and an i-th recording layer that is sensitive to light with a center wavelength λi to produce an i-th color different from the 1st, 2nd, . . . , and i−1-th colors; are layered in this order from the exposure light source side to the support. In this case, i is 2 or more, and an inequality of the center wavelength λ1<λ2< . . . <λi is satisfied.
Although the recording materials can be used for various purposes, image recording can be performed with a light source using ultraviolet or short wave visible light, but not with a compact and inexpensive, infrared laser or blue to red light source.
In a case where a compact and inexpensive, infrared laser or blue to red light source is used, the recording layer needs to contain a dye that can absorb each irradiated light in an ultraviolet to infrared region to form a fine image at high speed. However, when a dye that absorbs visible light is used, the background portion undergoes coloring, thereby resulting in a low quality image with poor contrast. On the other hand, when a dye that absorbs near-infrared light is used, the laser light source corresponding to the dye is expensive, although coloring in the background portion can be reduced.